4000 (the set-user-ID-on-execution bit) Executable files with this bit set will run with effective uid set to the uid of the file owner. Directories with the set-user-id bit set will force all files and sub-directories created in them to be owned by the directory owner and not by the uid of the creating process, if the underlying file system supports this feature: see chmod(2) and the suiddir option to mount(8). 2000 (the set-group-ID-on-execution bit) Executable files with this bit set will run with effective gid set to the gid of the file owner.